This invention relates to a method and apparatus for quantitatively determining the different forms of sulphur present in a matrix, such as coal, and is a continuation-in-part of U.S. application Ser. No. 809,737, filed Dec. 17, 1985.
One of the more serious environmental problems throughout the world is air pollution due to the emission of sulphur oxides when sulphur-containing fuels are burned. It is now widely recognized that sulphur oxides are particularly harmful pollutants, producing what is now known as acid rain.
Coal remains one of the world's most important fuel sources and large quantities are burned in thermogenerating plants for conversion into electrical energy. Many coals contain substantial amounts of sulphur which generate unacceptable amounts of sulphur oxides on burning. Coal combustion is by far the largest single source of sulphur dioxide pollution in the United States.
The sulphur content of coal, nearly all of which is emitted as sulphur dioxides during combustion, is present in essentially three forms: pyritic sulphur, organic sulphur and sulphate sulphur. Distribution between the different forms of sulphur varies widely among various coals and can even vary quite substantially within a single coal deposit.
It is, of course, highly desirable to be able to remove substantial portions of the sulphur present in coal before the coal is burned. Since the different forms of sulphur must be removed by different techniques, how a given supply of coal will be processed will be largely dependent on the relative proportions of the different forms of sulphur present in the coal. The present ASTM methods of analyzing for the different forms of sulphur present in coal are exceedingly time consuming and require highly trained personnel. For instance, the current practice utilizes wet analysis of pyritic and sulphatic sulphur to get the content of organic sulphur by difference from the total sulphur contents.
There are many different instruments available on the market that can quickly analyze the total sulphur content of coal. For instance, one commercial analyzer oxidizes the coal sample in a resistance furnace, where the sulphur in the coal is combusted to a gas of sulphur oxycompounds (SO.sub.x) which is detected by an infrared detector. These sulphur oxycompounds are primary sulphur dioxide together with minor amounts of other sulphur oxycompounds. However, this analyzer is capable only of giving the total infrared intensity, time integrated as the total sulphur content.
There is a need for a method and apparatus which can quantitatively determine the different forms of sulphur present in a matrix, such as coal, as simply as total sulphurs can now be determined. With that object in mind, the present inventors developed a method for quantitatively determining the different forms of sulphur present in a sulphur containing material, such as coal, in which a finely divided sulphur-containing sample was burned within a confined combustion chamber. This combustion chamber was at a predetermined elevated temperature, and the combustion gases from the combustion chamber were continuously removed. These removed combustion gases were passed through an infrared analyzer which continuously monitored the intensity of the infrared spectra for SO.sub.x in the combustion gases. The infrared intensity was measured as a function of evolution time of SO.sub.x from the coal sample to obtain peaks in an infrared intensity-time pattern indicative of different forms of sulphur. Based upon the shape of these pattern peaks and the area under the peaks, the quantity of each form of sulphur in the sample was determined.
The above study showed that the different forms of sulphur within coal or other matrix have sufficiently different oxidation or dissociation rates that these can be detected and measured on the basis of SO.sub.x emissions during oxidation. The different forms of sulphur can be shown as separate and distinct peaks on an infrared spectro-chronogram. Thus, the area under the total curve of such spectro-chronogram represents the total sulphur content of the sample and when the different peaks in the curve are resolved into individual curves, the areas under the individual curves can be identified with the amounts of the different forms of sulphur in the total sample. The multi-peak curve can be resolved into individual curves by known techniques utilizing microprocessor technology.
However, there was a major difficulty with the above procedure in that replicate spectro-chronograms on a common test sample varied widely in characteristics. This poor reproducibility of spectro-chronographic results made the deconvolution of different sulphur peaks virtually impossible.